A power chuck or mandrel such as described in my numerous earlier patents has a chuck or mandrel body centered on and rotatable about the axis of a headstock on which it is mounted. Normally jaws or similarly effective elements on the chuck body can be displaced radially by axial displacement of a central operating member. In a standard chuck this operating member may have a plurality of hooks with inclined faces that engage oppositely inclined faces of the jaws so that displacement of the hooks cams the jaws radially in or out depending on the axial displacement direction. In a power mandrel such as described in my copending application 370,957 filed April 22, 1982 the operating member is a piston which pressurizes the interior of an outwardly swellable sleeve that engages the inner surface of a tubular workpiece or of a bore in a workpiece or tool.
Commonly owned U.S. Pat. No. 3,641,875, which is roughly the equivalent of German Pat. No. 1,911,558 of Rudi Kodalle, describes a classic hydraulic or pneumatic actuator. In this arrangement the cylinder extends along a main axis and contains an axially displaceable piston that forms two compartments in the cylinder. The piston has an axially backwardly extending stem also centered on the axis and formed with respective intake passages each having one end opening into a respective one of the compartments and another end opening at a respective location on the stem. A connector is rotatable about the axis on the stem and is provided with respective fittings communicating with the locations. Bearings prevent the connector from moving axially on the stem.
Fluid can be fed under pressure alternately to the fittings to pressurize and depressurize the respective compartments and thereby axially displace the piston in the cylinder so that the cylinder can be connected to a chuck body and the piston to a chuck-actuating member for fluid actuation of the member. A double check valve arrangement is built right into the piston for inhibiting flow out of either of the compartments unless one of the passages is pressurized.
In this arrangement coacting sensor elements, normally a switch and a cam, are provided, one carried by and therefore axially linked to the piston and the other fixed to a stationary support. The switch is normally provided on the support at such a position that it is actuated when the piston reaches one end position. Another switch and/or cam may be provided for the other end position, so that an automatic controller will know when the operating member linked to the piston has reached an end position. This information is useful since the piston can normally only move into an end position when the jaws or the like it controls are not properly engaged with the workpiece or tool. Thus when this end position is reached the operator can be automatically signaled that something has gone wrong.
Such an arrangement is relatively simple since the connector which is also known as the distributor is normally fixed against rotation and therefore only moves slightly axially relative to the support. The device is disadvantageous in that it is relatively bulky. Furthermore it cannot be counted on to give an accurate response, unless the device is meticulously calibrated each time it is used. As there is frequently a slight shifting of the chuck to which the cylinder is secured, so that this displacement, depending on its direction, is added to or subtracted from the actual piston displacement.